KR102426798B1 - Non-aqueous electrolyte solution and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery comprising the same, and more particularly, to a lithium salt, a fluorine-based linear ether solvent, a fluorine-based cyclic carbonate solvent, and a fluorine-based lithium compound, wherein the fluorine-based linear ether solvent: a fluorine-based cyclic carbonate The solvent relates to a non-aqueous electrolyte for a lithium secondary battery contained in a weight ratio of 6:4 to 9:1, and a lithium secondary battery having improved high-temperature storage characteristics by including the same.

Description

Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery comprising same

The present invention relates to a non-aqueous electrolyte for a lithium secondary battery in which oxidation stability is secured and side reactions with an electrode are suppressed, and to a lithium secondary battery having improved high-temperature storage characteristics by including the same.

As personal IT devices and computer networks are developed due to the development of the information society, and the overall society's dependence on electric energy increases accordingly, technology development for efficiently storing and utilizing electric energy is required.

Among the technologies developed for this purpose, the most suitable technology for various uses is a secondary battery-based technology. Since secondary batteries can be miniaturized enough to be applied to personal IT devices and the like, and can also be applied to electric vehicles and power storage devices, interest in this is emerging. Among these secondary battery technologies, a lithium ion battery, which is a battery system with the highest theoretical energy density, is in the spotlight and is currently being applied to various devices.

Unlike the initial period when lithium metal was directly applied to the system, such a lithium ion battery consists of a positive electrode made of a transition metal oxide containing lithium, a negative electrode capable of storing lithium, an electrolyte, and a separator.

In the case of a double electrolyte, as it is known as a component that has a great influence on the stability and safety of a lithium ion battery, a lot of research is being conducted on this.

In the case of an electrolyte for a lithium ion battery, it is composed of a lithium salt, an organic solvent dissolving the same, and a functional additive, and proper selection of these components is important in order to improve the electrochemical properties of the battery.

On the other hand, in the case of a lithium secondary battery for a vehicle, it is required to have a high capacity and to be stably driven under a high temperature and a high voltage of 4.5V or more.

However, as carbonate-based organic solvents are mainly used as electrolyte solvents, when stored for a long time at high temperatures or driven under high voltages, side reactions with electrodes occur or irreversible capacity due to oxidative decomposition occurs, ensuring a satisfactory operating voltage. It is not easy to do.

Accordingly, in order to manufacture a lithium secondary battery having excellent stability under high temperature and high voltage, it is necessary to develop a non-aqueous electrolyte having high oxidation resistance.

Korean Patent Publication No. 2018-0089861

An object of the present invention is to provide a non-aqueous electrolyte for a lithium secondary battery in which oxidation stability is secured and side reactions with electrodes are suppressed.

In addition, an object of the present invention is to provide a lithium secondary battery having improved high-temperature storage characteristics by including the non-aqueous electrolyte for a lithium secondary battery.

In one embodiment of the present invention to achieve the above object,

lithium salt,

A fluorine-based linear ether solvent represented by the following formula (1);

a fluorine-based cyclic carbonate solvent, and

It contains a fluorine-based lithium compound represented by the following formula (2),

The fluorine-based linear ether solvent and the fluorine-based cyclic carbonate solvent are included in a weight ratio of 6:4 to 9:1 to provide a non-aqueous electrolyte for a lithium secondary battery.

[Formula 1]

R ₁ -OR ₂

In Formula 1,

R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms substituted or unsubstituted with an element fluorine, with the proviso that at least one of R ₁ and R ₂ is an alkyl group having 1 to 10 carbon atoms substituted with an element fluorine.

[Formula 2]

In Formula 2,

Y ₁ To Y ₄ are each independently O or S,

R ₃ and R ₄ are each independently hydrogen or fluorine.

In another embodiment of the present invention, there is provided a lithium secondary battery including the non-aqueous electrolyte for a lithium secondary battery of the present invention.

In the present invention, in order to prevent a side reaction between the electrode and the electrolyte at high temperature during charging and discharging or during storage, a non-aqueous electrolyte for a lithium secondary battery that contains a fluorine-based organic solvent and a fluorine-based lithium compound but does not contain a non-fluorine-based organic solvent can be provided. have. In addition, by including such a non-aqueous electrolyte, it is possible to implement a lithium secondary battery with improved high-temperature storage characteristics.

Hereinafter, the present invention will be described in more detail.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

Non-aqueous electrolyte for lithium secondary battery

According to the present specification, there is provided a non-aqueous electrolyte for a lithium secondary battery having a novel configuration, and the non-aqueous electrolyte includes a lithium salt, a fluorine-based linear ether solvent represented by the following Chemical Formula 1, a fluorine-based cyclic carbonate solvent, and a fluorine-based lithium compound represented by the following Chemical Formula 2 Including, wherein the fluorine-based linear ether solvent and the fluorine-based cyclic carbonate solvent are included in a weight ratio of 6:4 to 9:1 to provide a non-aqueous electrolyte for a lithium secondary battery.

[Formula 1]

R ₁ -OR ₂

In Formula 1,

R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms substituted or unsubstituted with an element fluorine, with the proviso that at least one of R ₁ and R ₂ is an alkyl group having 1 to 10 carbon atoms substituted with an element fluorine.

[Formula 2]

In Formula 2,

Y ₁ To Y ₄ are each independently O or S,

R ₃ and R ₄ are each independently hydrogen or fluorine.

At this time, the non-aqueous electrolyte for a lithium secondary battery of the present invention is characterized in that it does not contain a non-fluorine-based carbonate-based solvent as a non-aqueous electrolyte component.

(1) lithium salt

First, in the non-aqueous electrolyte for a lithium secondary battery of the present invention, the lithium salt may be used without limitation, those commonly used in the electrolyte for a lithium secondary battery, for example, Li ⁺ as a cation, F ^- as an anion, Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , ClO ₄ ^- , BF ₄ ^- , B ₁₀ Cl ₁₀ ^- , PF ₆ ^- , CF ₃ SO ₃ ^- , CH ₃ CO ₂ ^- , CF ₃ CO ₂ ^- , AsF ₆ ^- , SbF ₆ ^- , AlCl ₄ ^- , AlO ₄ ^- , CH ₃ SO ₃ ^- , BF ₂ C ₂ O ₄ ^- , BC ₄ O ₈ ^- , PF ₄ C ₂ O ₄ ^- , PF ₂ C ₄ O ₈ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , C ₄ F ₉ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (FSO ₂ ) ₂ N ^- , (CF ₃ SO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , ( At least one selected from the group consisting of SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- can be heard

Specifically, the lithium salt is LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiAlO ₄ , LiCH ₃ SO ₃ , LiFSI (lithium fluorosulfonyl imide, LiN(SO ₂ F) ₂ ), LiTFSI (lithium (bis)trifluoromethanesulfonimide, LiN(SO ₂ CF ₃ ) ₂ ) and LiBETI (lithium bisperfluoroethanesulfonimide, LiN(SO) ₂ C ₂ F ₅ ) ₂ ) may include a single substance or a mixture of two or more selected from the group consisting of. More specifically, the lithium salt may include a single material or a mixture of two or more selected from the group consisting of LiBF ₄ , LiPF ₆ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiFSI, LiTFSI, and LiBETI. In addition to these, lithium salts commonly used in electrolytes for lithium secondary batteries may be used without limitation.

The lithium salt may be appropriately changed within the range that can be used in general, but to be included in the electrolyte at a concentration of 0.8 M to 4.0 M, specifically, at a concentration of 1.0M to 3.0M, in order to obtain an optimal effect of forming a film for preventing corrosion of the electrode surface. can

If the concentration of the lithium salt is less than 0.8M, the effect of improving the low-temperature output of the lithium secondary battery and improving the cycle characteristics during high-temperature storage is insignificant. can

(2) Fluorine solvents

According to the present specification, the non-aqueous electrolyte for a lithium secondary battery includes a fluorine-based solvent as a main solvent.

The fluorine-based solvent may include a fluorine-based linear ether solvent and a fluorine-based cyclic carbonate solvent represented by the following Chemical Formula 1,

[Formula 1]

R ₁ -OR ₂

In Formula 1,

R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms substituted or unsubstituted with an element fluorine, with the proviso that at least one of R ₁ and R ₂ is an alkyl group having 1 to 10 carbon atoms substituted with an element fluorine.

Meanwhile, in Formula 1, R ₁ and R ₂ are each independently an alkyl group having 2 to 8 carbon atoms substituted or unsubstituted with a fluorine element, with the proviso that at least one of R ₁ and R ₂ has 2 to carbon atoms substituted with an element fluorine 8 may be an alkyl group. Specifically, in Formula 1, R ₁ and R ₂ are each independently an alkyl group having 2 to 5 carbon atoms substituted or unsubstituted with a fluorine element, provided that at least one of R ₁ and R ₂ has 2 carbon atoms substituted with an element fluorine It may be an alkyl group of to 5.

More specifically, the fluorine-based linear ether solvent is 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether (TFETFEE), 1,1,2,2-tetrafluoroethyl 2 ,2,3,3-tetrafluoropropyl ether (TFETFPE) and 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (or 1H,1H,5H-perfluoro It may be at least one selected from the group consisting of pentyl 1,1,2,2-tetrafluoroethyl ether), specifically 1,1,2,2-tetrafluoroethyl 2,2,3; 3-tetrafluoropropyl ether.

In addition, the fluorine-based cyclic carbonate solvent may be fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC), and specifically, fluoroethylene carbonate may be mentioned.

Currently, most secondary batteries use a non-fluorine-based carbonate solvent as the main solvent of the non-aqueous electrolyte. These solvents are generally stored at high temperatures for a long time, causing gas to be generated due to oxidation of the electrolyte, causing swelling, etc. The stable structure of the battery There is a problem in transforming Moreover, the reaction heat generated by the side reaction between the electrode and the non-fluorine-based carbonate solvent raises the internal temperature of the battery, and when the temperature reaches a temperature above the ignition point, it combines with surrounding oxygen and leads to a thermal-run away phenomenon. There is a problem in that the secondary battery ignites and explodes.

Therefore, in the present invention, the non-aqueous electrolyte solvent does not contain a non-fluorine-based carbonate solvent having unstable oxidation stability, but contains only a fluorine-based solvent having excellent electrochemical stability as the non-aqueous electrolyte main solvent. That is, since the fluorine-based solvent has high oxidation stability and forms stable LiF even under high voltage in the film component, side reaction between the non-aqueous electrolyte and the electrode, especially the positive electrode, is prevented during operation (charge/discharge) under high voltage or during storage at high temperature. can be prevented

The fluorine-based solvent may include a fluorine-based linear ether solvent and a fluorine-based cyclic carbonate solvent as main solvents.

That is, the fluorine-based cyclic ether solvent may contribute to the improvement of the dielectric constant by many cyclic solvents in the electrolyte, but has a disadvantage in that the mobility of lithium ions is weakened while exhibiting high viscosity physical properties. Accordingly, it is preferable to use a fluorine-based linear ether solvent instead of a fluorine-based cyclic ether solvent in order to secure high ionic conductivity properties. In addition, it is preferable to use a fluorine-based cyclic carbonate solvent having a higher dielectric constant than that of the fluorine-based linear carbonate solvent.

On the other hand, the fluorine-based linear ether solvent and the fluorine-based cyclic carbonate solvent are mixed and included in a weight ratio of 6:4 to 9:1, specifically 7:3 to 9:1, and more specifically, 8:2 to 9:1 by weight, high voltage and performance improvement effect when stored at a high temperature.

In the present invention, the dielectric constant of the non-aqueous electrolyte is increased by using a combination of a fluorine-based linear ether solvent and a fluorine-based cyclic carbonate solvent in the above range as the main solvent of the non-aqueous electrolyte to secure high ionic conductivity properties of the lithium secondary battery, and based on this, the dielectric constant of the lithium secondary battery is increased. As the degree of dissociation of the salt increases, the ionic conductivity performance of the electrolyte can be secured. If the weight ratio of the fluorine-based linear ether solvent is less than 6, that is, if the weight ratio of the fluorine-based cyclic carbonate solvent is greater than 4, the physical properties of the non-aqueous electrolyte may become highly viscous and the mobility of lithium ions may be reduced. In addition, when the weight ratio of the fluorine-based linear ether solvent exceeds 9, that is, when the weight ratio of the fluorine-based cyclic carbonate solvent is less than 1, the dielectric constant of the non-aqueous electrolyte is lowered, thereby reducing the degree of dissociation of the lithium salt.

(3) Fluorine-based lithium compounds

In addition, according to the present specification, the non-aqueous electrolyte for a lithium secondary battery of the present invention includes a fluorine-based lithium compound represented by the following Chemical Formula 2 as an additive.

[Formula 2]

In Formula 2,

Y ₁ To Y ₄ are each independently O or S,

R ₃ and R ₄ are each hydrogen or fluorine.

The fluorine-based lithium compound is a compound that can give a synergistic effect to the performance improvement of the lithium secondary battery of the fluorine-based linear ether solvent as described above, and can form a uniform and thin film on the positive electrode and the negative electrode.

That is, the fluorine-based lithium compound mainly acts on the formation of the positive electrode SEI film to reduce the positive electrode reaction of other materials to form a uniform and thin film, thereby improving the durability of the battery. In addition, the fluorine-based lithium compound may serve as a complement in forming an SEI film on the surface of the negative electrode in addition to the effect expressed by the fluorine-based preceding ether solvent, and may serve to inhibit the decomposition of the solvent in the electrolyte, The mobility of lithium ions can be improved.

Specifically, the fluorine-based lithium compound may be a compound represented by the following Chemical Formula 2a.

[Formula 2a]

Meanwhile, the fluorine-based lithium compound may be appropriately used depending on the amount of the non-aqueous electrolyte additive generally added to the non-aqueous electrolyte, for example, 0.05 wt % to 3.0 wt %, based on the total weight of the non-aqueous electrolyte for lithium secondary batteries, specifically As may be included in 0.1 wt% to 1.0 wt%.

When the fluorine-based lithium compound is included in the above range, a strong SEI film can be stably formed on the positive electrode and the negative electrode, and the effect thereof can be obtained.

If the content of the fluorine-based lithium compound is less than 0.05% by weight, the effect of forming a film by the additive may be insignificant. .

Therefore, when the additive is contained in an amount of 0.05 wt% or more, specifically 0.1 wt% or more, and 3 wt% or less, specifically 1.0 wt%, the disadvantages such as side reactions, capacity reduction and resistance increase due to the additive are maximized. While suppressing, it is possible to realize the effect of forming a stable film on the surface of the anode and the cathode.

(4) Fluorine solvents

Meanwhile, the non-aqueous electrolyte for a lithium secondary battery according to the present specification may further include a fluorine-based solvent.

The fluorine-based solvent is at least one selected from the group consisting of a fluorine-based linear carbonate solvent, a fluorine-based dioxolane solvent, a fluorine-based phosphite solvent, a fluorine-based phosphate solvent, a fluorine-based benzene solvent, a fluorine-based cyclic ether solvent, a fluorine-based propionate solvent, and a fluorine-based acetate solvent can be heard

The fluorine-based linear carbonate solvent is at least one selected from the group consisting of fluorodimethyl carbonate (F-DMC), fluoroethyl methyl carbonate (FEMC) and methyl 2,2,2-trifluoroethyl carbonate (F3-EMC). can be heard

In addition, the fluorine-based dioxolane solvent may include 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL).

The fluorine-based phosphite solvent may include tris (trifluoroethyl) phosphite (TFEPi).

The fluorine-based phosphate solvent may include tris(2,2,2-trifluoroethyl)phosphate (TFEPa).

The fluorine-based benzene solvent may include at least one selected from the group consisting of monofluorobenzene (FB), difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentatrifluorobenzene, and hexafluorobenzene. .

The fluorine-based propionate solvent is methyl 3,3,3-trifluoropropionate (3-FMP), methyl 2,3,3,3-tetrafluoropropionate (4-FMP) and methyl pentafluoro At least one selected from the group consisting of propionate may be mentioned.

The fluorine-based acetate-based solvent may include at least one selected from the group consisting of methyl difluoroacetate, ethyl difluoroacetate, and difluoroethyl acetate.

Meanwhile, in the non-aqueous electrolyte for a lithium secondary battery of the present invention, the weight ratio of the mixed solvent of the fluorine-based linear ether solvent and the fluorine-based cyclic carbonate solvent to the fluorine-based solvent may be 1:0 to 1:1.

When such a ratio range is satisfied, an improvement in high-temperature storage characteristics can be expected by improving capacity retention at high temperatures and suppressing gas generation during high-temperature storage. That is, by controlling the weight ratio of the mixed solvent of the fluorine-based linear ether solvent and the fluorine-based cyclic carbonate solvent and the fluorine-based solvent additionally included, a non-aqueous electrolyte that can satisfy both battery performance and cycle characteristics at high temperature and high voltage can be implemented, This may be more likely to be implemented as it falls within a preferred range among the above ranges.

(5) fluorinated compounds

The non-aqueous electrolyte for a lithium secondary battery according to the present specification may further include other fluorinated compounds in addition to the fluorinated lithium compound represented by Formula 2 above.

The fluorinated compound is a compound that can give a synergistic effect to the performance improvement of a lithium secondary battery of the fluorine-based lithium compound represented by Chemical Formula 2 as described above, and generally includes at least one element of fluorine applied to the non-aqueous electrolyte of a lithium secondary battery. Additives containing may be applied.

Specifically, the fluorinated compound may include at least one selected from the group consisting of a fluorinated nitrile-based compound, a fluorinated lithium-type phosphate-based compound, and a fluorinated lithium-type borate-based compound.

In this case, the fluorinated nitrile-based compound may include at least one selected from the group consisting of 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, and trifluorobenzonitrile.

The lithium fluorinated phosphate-based compound may include at least one selected from the group consisting of lithium difluoro(bisoxalato)phosphate and lithium difluorophosphate (LiPO ₂ F ₂ ).

The lithium fluoride-type borate-based compound is from the group consisting of lithium tetrafluoroborate (LiBF ₄ ) and lithium difluoro (oxalato) borate (LiODFB), except for the fluorine-based lithium compound represented by Formula 2 above. at least one or more selected.

The fluorinated compound may be used in a mixture of two or more, and is included in an amount of 10 wt% or less, specifically 0.05 wt% to 5.0 wt%, more specifically 0.1 wt% to 5.0 wt%, based on the total weight of the non-aqueous electrolyte for a secondary battery can

When the content of the fluorinated compound exceeds 10% by weight, there is a possibility that side reactions in the electrolyte may be excessively generated during charging and discharging of the battery. In particular, when an excessive amount of the fluorinated compounds is added, they are not sufficiently decomposed at high temperatures, so that they exist as unreacted or precipitated substances in the electrolyte at room temperature. Therefore, side reactions in which the lifespan or resistance characteristics of the secondary battery are lowered may occur. On the other hand, if the content of the fluorinated compound is less than 0.05 wt %, effects such as low-temperature output improvement and high-temperature storage characteristics and high-temperature lifespan characteristics of the battery to be improved according to the use of the fluorinated compound may be insignificant.

(6) Others

On the other hand, the non-aqueous electrolyte for a lithium secondary battery according to the present specification is characterized in that it does not contain a non-fluorine-based carbonate-based solvent. Specifically, the non-fluorine-based carbonate-based solvent may be a cyclic carbonate-based organic solvent or a linear carbonate-based organic solvent.

The cyclic carbonate-based organic solvent is a high-viscosity organic solvent, and specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, and 1,2-pentylene. carbonate, 2,3-pentylene carbonate or vinylene carbonate.

The linear carbonate-based organic solvent is an organic solvent having a low viscosity and a low dielectric constant, and representative examples thereof include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC) , methylpropyl carbonate or ethylpropyl carbonate.

Since the non-fluorine-based carbonate-based solvent has low oxidation stability, gas may be generated due to a side reaction with the electrode during high-temperature storage or high-voltage driving, thereby impairing the stability of the lithium secondary battery. Therefore, it is preferable not to include a non-fluorine-based carbonate-based solvent in the non-aqueous electrolyte in terms of improving the performance of the secondary battery.

lithium secondary battery

Further, in another embodiment of the present invention, there is provided a lithium secondary battery including the non-aqueous electrolyte for a lithium secondary battery of the present invention.

On the other hand, the lithium secondary battery of the present invention may be manufactured according to a conventional method known in the art, and specifically, a positive electrode, a negative electrode, and an electrode assembly in which a separator is sequentially stacked between the positive electrode and the negative electrode is formed in the battery case. After accommodating, the non-aqueous electrolyte of the present invention may be added thereto. Each component constituting the lithium secondary battery is as described below.

(1) Anode

The positive electrode may be prepared by coating a positive electrode slurry including a positive electrode active material, a binder, a conductive material and a solvent on a positive electrode current collector, followed by drying and rolling.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon on the surface of aluminum or stainless steel. , nickel, titanium, silver, etc. may be used.

The positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically may include a lithium composite metal oxide including lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. have. More specifically, the lithium composite metal oxide is a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O ₄ , etc.), a lithium-cobalt-based oxide (eg, LiCoO ₂ , etc.), lithium-nickel-based oxide (eg, LiNiO ₂ ), lithium-nickel-manganese oxide (eg, LiNi _1-Y Mn _Y O ₂ (0<Y<1), LiMn _2-z Ni _z O ₄ (0<Z) <2), lithium-nickel-cobalt-based oxide (eg, LiNi _1-Y1 Co _Y1 O ₂ (0<Y1<1), lithium-manganese-cobalt-based oxide (eg, LiCo _1-Y2 Mn _Y2 ) O ₂ (0<Y2<1), LiMn _2-z1 Co _z1 O ₄ (0<Z1<2), lithium-nickel-manganese-cobalt oxide (eg, Li(Ni _p Co _q Mn _r1 )O ₂ (0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (0<p1<2, 0 < q1 <2, 0 <r2<2, p1+q1+r2=2), or lithium-nickel-cobalt-transition metal (M) oxide (eg, Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ ( M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of each independent element, 0 < p2 < 1, 0 < q2 <1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1), and the like, and any one or two or more of these compounds may be included. In terms of improving properties and stability, the lithium composite metal oxide is LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , lithium nickel manganese cobalt oxide (eg, Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , etc.), or lithium nickel cobalt aluminum oxide (eg, Li(Ni _0.8 Co _0.15 Al _0.05 )O ₂ , etc.) ), and the like, considering the significant improvement effect by controlling the type and content ratio of the element forming the lithium composite metal oxide, the lithium composite metal oxide is Li(Ni _0.6 Mn _0.2 Co _0.2 )O ₂ , Li(Ni _0.5 Mn _0.3 Co _0.2 )O ₂ , Li(Ni _0.7 Mn _0.15 Co _0.15 )O ₂ , or Li(Ni _0.8 Mn _0.1 Co _0.1 )O ₂ , and the like, and any one or a mixture of two or more thereof may be used. have.

The positive active material may be included in an amount of 80 wt% to 99 wt%, specifically, 90 wt% to 99 wt%, based on the total weight of the solid content in the cathode slurry. In this case, when the content of the positive electrode active material is 80% by weight or less, the energy density may be lowered, and thus the capacity may be lowered.

The binder is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the solid content in the positive electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene ether monomer, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

In addition, the conductive material is a material that imparts conductivity without causing a chemical change to the battery, and may be added in an amount of 1 to 20 wt % based on the total weight of the solid content in the positive electrode slurry.

Representative examples of such a conductive material include carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; Graphite powder, such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

In addition, the solvent may include an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount having a desirable viscosity when the positive electrode active material and, optionally, a binder and a conductive material are included. For example, it may be included so that the solid content concentration in the positive electrode slurry including the positive electrode active material and optionally the binder and the conductive material is 10% by weight to 60% by weight, preferably 20% by weight to 50% by weight.

(2) cathode

The negative electrode may be prepared by coating a negative electrode slurry including a negative electrode active material, a binder, a conductive material and a solvent on a negative electrode current collector, and then drying and rolling.

The negative electrode current collector generally has a thickness of 3 to 500 μm. Such a negative current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel. The surface treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. may be used. In addition, like the positive electrode current collector, the bonding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven body.

In addition, the negative electrode active material is lithium metal, a carbon material capable of reversibly intercalating/deintercalating lithium ions, a metal or an alloy of these metals and lithium, a metal composite oxide, lithium doping and de-doping. It may include at least one selected from the group consisting of materials and transition metal oxides.

As a carbon material capable of reversibly intercalating/deintercalating lithium ions, any carbon-based negative active material generally used in lithium ion secondary batteries may be used without particular limitation, and representative examples thereof include crystalline carbon, Amorphous carbon or these may be used together. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low temperature calcined carbon). or hard carbon, mesophase pitch carbide, and calcined coke.

Examples of the above metals or alloys of these metals and lithium include Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al. And a metal selected from the group consisting of Sn or an alloy of these metals and lithium may be used.

Examples of the metal composite oxide include PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ . , Bi ₂ O ₅ , Li _x Fe ₂ O ₃ (0≤x≤1), Li _x WO ₂ (0≤x≤1) and Sn _x Me _1-x Me' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, a group 1, 2, or 3 element of the periodic table, halogen; 0<x≤1;1≤y≤3; 1≤z≤8) One selected from may be used.

Examples of the material capable of doping and dedoping lithium include Si, SiO _x (0<x≤2), Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, An element selected from the group consisting of rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-Y (wherein Y is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a transition metal, a rare earth) It is an element selected from the group consisting of elements and combinations thereof, and is not Sn) and the like. Also, at least one of these and SiO ₂ may be mixed and used. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, It may be selected from the group consisting of Te, Po, and combinations thereof.

Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, and lithium vanadium oxide.

The negative active material may be included in an amount of 80% to 99% by weight based on the total weight of the solids in the negative electrode slurry.

The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the solid content in the negative electrode slurry. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, and polyethylene, polypropylene, ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 1 to 20 wt% based on the total weight of the solid content in the negative electrode slurry. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and for example, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black. carbon powder; Graphite powder, such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The solvent may include water or an organic solvent such as NMP, alcohol, or the like, and may be used in an amount to achieve a desirable viscosity when the negative electrode active material and, optionally, a binder and a conductive material are included. For example, the solid content concentration in the slurry including the negative electrode active material and optionally the binder and the conductive material may be 50 wt% to 75 wt%, preferably 50 wt% to 65 wt%.

(3) separator

The separator included in the lithium secondary battery of the present invention is a conventional porous polymer film generally used, for example, ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate. A porous polymer film made of a polyolefin-based polymer such as a copolymer may be used alone or by laminating them, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fiber, polyethylene terephthalate fiber, etc. may be used. However, the present invention is not limited thereto.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a prismatic shape, a pouch type, or a coin type.

Hereinafter, examples will be given to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example

Example 1.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether: fluoroethylene carbonate was mixed in a 7:3 weight ratio, and LiPF ₆ was dissolved so as to be 1.2M, a fluorine-based solvent was prepared. 0.1 g of the compound represented by Formula 2a was added to 99.9 g of the fluorine-based organic solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

(Manufacture of lithium secondary battery)

A cathode active material (LiNi _0.6 Co _0.2 Mn _0.2 O ₂ ; NCM) a conductive material (carbon black) and a binder (polyvinylidene fluoride) in a weight ratio of 97.5:1:1.5 to N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode slurry (solid content: 50% by weight). The positive electrode slurry was applied and dried on an aluminum (Al) thin film as a positive electrode current collector having a thickness of 12 μm, and then a roll press was performed to prepare a positive electrode.

A negative electrode active material (SiO: graphite = 5:95 weight ratio), binder (SBR-CMC), and a conductive material (carbon black) were added to water as a solvent in a 95:3.5:1.5 weight ratio to slurry the negative electrode mixture (solid content: 60% by weight) ) was prepared. The negative electrode mixture slurry was applied to a 6 μm-thick copper (Cu) thin film as a negative electrode current collector and dried, and then a roll press was performed to prepare a negative electrode.

The positive electrode, the inorganic particle (Al ₂ O ₃ ) coated polyolefin-based porous separator, and the negative electrode were sequentially stacked to prepare an electrode assembly.

A pouch-type lithium secondary battery was manufactured by accommodating the assembled electrode assembly in a pouch-type battery case, and injecting the non-aqueous electrolyte for the lithium secondary battery.

Example 2.

A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that 1 g of the compound represented by Formula 2a was added to 99 g of a fluorine-based solvent to prepare a non-aqueous electrolyte for a lithium secondary battery. (See Table 1 below).

Example 3.

A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that 3 g of the compound represented by Formula 2a was added to 97 g of a fluorine-based solvent to prepare a non-aqueous electrolyte for a lithium secondary battery. (See Table 1 below).

Example 4.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

Fluorine-based mixed solvent (1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether:fluoroethylene carbonate = 7:3 weight ratio) and methyl 2,2,2-trifluoro Roethyl carbonate was mixed in a weight ratio of 1:0.7, and LiPF ₆ was dissolved to 1.2M to prepare a fluorine-based solvent. 1 g of the compound represented by Formula 2a was added to 99 g of the fluorine-based solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

(Manufacture of lithium secondary battery)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared non-aqueous electrolyte for a lithium secondary battery was injected.

Example 5.

A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same were prepared in the same manner as in Example 4, except that fluorobenzene was used instead of the methyl 2,2,2-trifluoroethyl carbonate (below See Table 1).

Example 6.

In the same manner as in Example 4 except for using methyl 3,3,3-trifluoropropionate instead of methyl 2,2,2-trifluoroethyl carbonate, a non-aqueous electrolyte for a lithium secondary battery and the same A lithium secondary battery was prepared including (see Table 1 below).

Example 7.

A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that 1 g of the compound represented by Formula 2a and 2 g of LiBF ₄ were added to 97 g of the fluorine-based solvent (Table 1 below). Reference).

Example 8.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether: fluoroethylene carbonate was mixed in a weight ratio of 6:4, and LiPF ₆ was dissolved to 1.2M to obtain a fluorine-based solvent. was prepared. 1 g of the compound represented by Formula 2a was added to 99 g of the fluorine-based organic solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

(Manufacture of lithium secondary battery)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared non-aqueous electrolyte for a lithium secondary battery was injected.

Example 9.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether: fluoroethylene carbonate was mixed in a weight ratio of 9:1, and LiPF ₆ was dissolved to 1.2M to obtain a fluorine-based solvent. was prepared. 1 g of the compound represented by Formula 2a was added to 99 g of the fluorine-based organic solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

(Manufacture of lithium secondary battery)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared non-aqueous electrolyte for a lithium secondary battery was injected.

Example 10.

A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that 4 g of the compound represented by Formula 2a was added to 96 g of the fluorine-based solvent (see Table 1 below).

Comparative Example 1.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

Ethylene carbonate: ethylmethyl carbonate was mixed in a weight ratio of 3:7, and LiPF ₆ was dissolved to 1.2M to prepare a fluorine-free solvent. 1 g of the compound represented by Formula 2a was added to 99 g of the non-fluorine-based organic solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

(Manufacture of lithium secondary battery)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared non-aqueous electrolyte for a lithium secondary battery was injected.

Comparative Example 2.

A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same were prepared in the same manner as in Comparative Example 1, except that 1 g of the compound represented by Formula 2a and 2 g of LiBF ₄ were added to 97 g of the non-fluorine-based organic solvent (below See Table 1).

Comparative Example 3.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether: ethylene carbonate: ethylmethyl carbonate was mixed in a 4:3:3 weight ratio, and LiPF ₆ was added to 1.2M. Dissolved to prepare a mixed solvent. 1 g of the compound represented by Formula 2a was added to 99 g of the mixed solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

(Manufacture of lithium secondary battery)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared non-aqueous electrolyte for a lithium secondary battery was injected.

Comparative Example 4.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether: ethylene carbonate was mixed in a 7:3 weight ratio, and LiPF ₆ was dissolved to 1.2M to prepare a mixed solvent did. 1 g of the compound represented by Formula 2a and 2 g of LiBF ₄ were added to 97 g of the mixed solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

(Manufacture of lithium secondary battery)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared non-aqueous electrolyte for a lithium secondary battery was injected.

Comparative Example 5.

A non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery including the same were prepared in the same manner as in Example 1, except that 2 g of LiBF ₄ was added to 98 g of a fluorine-based solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (Table 1 below) Reference).

Comparative Example 6.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

Instead of including a fluorine-based linear ether solvent, fluoroethylene carbonate: methyl 2,2,2-trifluoroethyl carbonate was mixed in a weight ratio of 1:0.7, and LiPF ₆ was dissolved to 1.2M to prepare a fluorine-based solvent. 1 g of the compound represented by Formula 2a and 2 g of LiBF ₄ were added to 97 g of the fluorine-based solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below).

(Manufacture of lithium secondary battery)

A lithium secondary battery was manufactured in the same manner as in Example 1, except that the prepared non-aqueous electrolyte for a lithium secondary battery was injected.

Comparative Example 7.

(Manufacture of non-aqueous electrolyte for lithium secondary battery)

1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether: fluoroethylene carbonate was mixed in a weight ratio of 5:5, and LiPF ₆ was dissolved to 1.2M to obtain a fluorine-based solvent. was prepared. A lithium secondary battery including the same was prepared in the same manner as in Example 1, except that 1 g of the compound represented by Formula 2a was added to 99 g of the fluorine-based solvent to prepare a non-aqueous electrolyte for a lithium secondary battery (see Table 1 below) ).

Comparative Example 8.

A non-aqueous electrolyte for a lithium secondary battery was carried out in the same manner as in Example 1, except that lithium difluoro bis(oxlato) phosphate (LiDFOP) was added instead of the compound of Formula 2a as a fluorine-based lithium compound. and a lithium secondary battery including the same (see Table 1 below).

In Table 1 below, the abbreviations of the compounds mean the following, respectively.

TFETFPE: 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropylether

FEC: fluoroethylene carbonate

F3-EMC: methyl 2,2,2-trifluoroethyl carbonate

3-FMP: methyl 3,3,3-trifluoropropionate,

FB: monofluorobenzene

EC: ethylene carbonate

EMC: ethylmethyl carbonate

LiBF ₄ : Lithium tetrafluoroborate

Experimental example

Experimental Example 1. Evaluation of high-temperature cycle characteristics

Each of the lithium secondary batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 3 and Comparative Examples 5 to 8 was charged under constant current/constant voltage conditions at 45° C. , 0.5C and 3.0V were discharged, 100 cycles were performed by using this as 1 cycle, and the discharge capacity of the last 100 cycles was confirmed.

The discharge capacity for each of the obtained lithium secondary batteries was expressed as a percentage (%) compared to the theoretical design capacity (110mAh), and is shown in Table 2 below.

45℃, capacity after 100 cycles (mAh) Capacity retention rate (%) Example 1 99.9 90.8 Example 2 102.9 93.5 Example 3 98.1 89.2 Example 4 104.7 95.2 Example 5 104.3 94.8 Example 6 103.0 93.6 Example 7 105.3 95.7 Example 8 101.1 91.9 Example 9 97.7 88.8 Example 10 96.1 87.4 Comparative Example 1 85.4 77.6 Comparative Example 2 90.3 82.1 Comparative Example 3 93.5 85.0 Comparative Example 5 95.5 86.8 Comparative Example 6 88.2 80.2 Comparative Example 7 87.5 79.5 Comparative Example 8 94.2 85.6

As shown in Table 2, in the case of the secondary batteries of Examples 1 to 10, it can be seen that all of the capacity retention ratio is excellent at about 87.4% or more. On the other hand, it can be seen that the secondary batteries of Comparative Examples 1 to 3 and Comparative Examples 5 to 8 have a capacity retention rate of 86.8% or less, which is lower than that of the secondary batteries of Examples 1 to 10.

On the other hand, in the case of the secondary battery of Example 10 having the non-aqueous electrolyte contained in an excess of the compound of Formula 2a, the cycle capacity retention rate is slightly reduced compared to the secondary batteries of Examples 1 to 9.

Experimental Example 2. Evaluation of high temperature storage characteristics

Each of the lithium secondary batteries prepared in Examples 1 to 10 and Comparative Examples 1 to 8 was charged at a rate of 0.7C to 4.4V under constant current/constant voltage conditions and 0.05C cut-off charging was performed once, and was heated in an oven at 85°C for 8 hours. stored for a while. Then, after discharging to 0.2C rate, 3.0V at 25 ℃, the capacity was measured.

The obtained capacity retention rate is shown in Table 3 below as a percentage (%) compared to the theoretical design capacity (110mAh).

Capacity after storage at 85℃ (mAh) Capacity retention rate (%) Example 1 95.3 86.6 Example 2 98.1 89.2 Example 3 97.8 88.9 Example 4 99.4 90.4 Example 5 101.5 92.3 Example 6 98.6 89.6 Example 7 99.7 90.6 Example 8 94.4 85.8 Example 9 100.8 91.6 Example 10 95.8 87.1 Comparative Example 1 82.7 75.2 Comparative Example 2 84.8 77.1 Comparative Example 3 89.4 81.3 Comparative Example 4 92.2 83.8 Comparative Example 5 93.6 85.1 Comparative Example 6 75.0 68.2 Comparative Example 7 70.1 63.7 Comparative Example 8 92.3 83.9

As shown in Table 3, in the case of the secondary batteries of Examples 1 to 10, it can be seen that the capacity retention rate after high-temperature storage is about 85.8% or more, which is excellent in all of them.

On the other hand, it can be seen that the secondary batteries of Comparative Examples 1 to 8 have a capacity retention rate of 85.1% or less after storage at high temperature, which is lower than that of the secondary batteries of Examples 1 to 10.

On the other hand, in the case of the secondary battery of Example 10 having the non-aqueous electrolyte containing an excess of the compound of Formula 2a and the secondary battery of Example 1 having the non-aqueous electrolyte containing the compound of Formula 2 in a small amount, Example 2 It can be seen that the cycle capacity retention rate is slightly lowered compared to the secondary batteries of Examples 7 to 9.

On the other hand, since FEC, which is a fluorine-based cyclic carbonate solvent, has a function of forming a film on the negative electrode, in the case of the lithium secondary battery of Example 8 having a non-aqueous electrolyte having a high FEC content, the same lifespan characteristic evaluation as in Experimental Example 1 performance improvement can be expected as the content increases. However, since there is a disadvantage in that the FEC is easily decomposed and the generation of CO ₂ gas is increased when exposed to a high temperature for a long time when stored at a high temperature, in the case of the lithium secondary battery of Example 8 having a non-aqueous electrolyte having a high FEC content, the example It can be seen that the capacity retention rate is somewhat inferior when stored at a high temperature compared to the lithium secondary batteries of 1 to 7 and 9.

Claims (14)

lithium salt,
An organic solvent comprising a fluorine-based linear ether solvent and a fluorine-based cyclic carbonate solvent represented by the following formula (1), and
Including a fluorine-based lithium compound represented by the following formula (2),
The fluorine-based linear ether solvent and the fluorine-based cyclic carbonate solvent are included in a weight ratio of 6:4 to 9:1,
The organic solvent is a non-aqueous electrolyte for a lithium secondary battery that does not contain a non-fluorine-based organic solvent.
[Formula 1]
R ₁ -OR ₂
In Formula 1,
R ₁ and R ₂ are each independently an alkyl group having 1 to 10 carbon atoms substituted or unsubstituted with an element fluorine, with the proviso that at least one of R ₁ and R ₂ is an alkyl group having 1 to 10 carbon atoms substituted with an element fluorine.

[Formula 2]

In Formula 2,
Y ₁ To Y ₄ are each independently O or S,
R ₃ and R ₄ are each independently hydrogen or fluorine.
The method according to claim 1,
In Formula 1, R ₁ and R ₂ are each independently an alkyl group having 2 to 8 carbon atoms that is unsubstituted or substituted with an elemental fluorine, provided that at least one of R ₁ and R ₂ is an alkyl group having 2 to 8 carbon atoms substituted with an element of fluorine A non-aqueous electrolyte for lithium secondary batteries with an alkyl group.
3. The method according to claim 2,
In Formula 1, R ₁ and R ₂ are each independently an alkyl group having 2 to 5 carbon atoms substituted or unsubstituted with an element of fluorine, provided that at least one of R ₁ and R ₂ is substituted with an element of fluorine, having 2 to 5 carbon atoms A non-aqueous electrolyte for a lithium secondary battery that is an alkyl group.
The method according to claim 1,
The fluorine-based linear ether solvent is 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3- A non-aqueous electrolyte for a lithium secondary battery which is at least one selected from the group consisting of tetrafluoropropyl ether and 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether.
The method according to claim 1,
The fluorine-based linear ether solvent is 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether non-aqueous electrolyte for a secondary battery.
The method according to claim 1,
The fluorine-based cyclic carbonate solvent is a non-aqueous electrolyte for a lithium secondary battery that is fluoroethylene carbonate or difluoroethylene carbonate.
The method according to claim 1,
The fluorine-based cyclic carbonate solvent is a non-aqueous electrolyte for a lithium secondary battery that is fluoroethylene carbonate.
The method according to claim 1,
The fluorine-based linear ether solvent: the fluorine-based cyclic carbonate solvent is a non-aqueous electrolyte for a lithium secondary battery that is included in a weight ratio of 7:3 to 9:1.
The method according to claim 1,
The fluorine-based lithium compound is a non-aqueous electrolyte for a lithium secondary battery that is a compound represented by the following formula (2a).
[Formula 2a]

The method according to claim 1,
The fluorine-based lithium compound is contained in an amount of 0.05 wt% to 3.0 wt% based on the total weight of the non-aqueous electrolyte for a lithium secondary battery.
The method according to claim 1,
The non-aqueous electrolyte for lithium secondary batteries is selected from the group consisting of a fluorine-based linear carbonate solvent, a fluorine-based dioxolane solvent, a fluorine-based phosphite solvent, a fluorine-based phosphate solvent, a fluorine-based benzene solvent, a fluorine-based cyclic ether solvent, a fluorine-based propionate solvent, and a fluorine-based acetate solvent A non-aqueous electrolyte for a lithium secondary battery further comprising at least one fluorine-based solvent.
12. The method of claim 11,
The mixed solvent of the fluorine-based linear ether solvent and the fluorine-based cyclic carbonate solvent: The weight ratio of the fluorine-based solvent is 1:0 to 1:1 for a lithium secondary battery non-aqueous electrolyte.
The method according to claim 1,
The non-aqueous electrolyte for a lithium secondary battery further comprises at least one fluorinated compound selected from the group consisting of a fluorinated nitrile-based compound, a fluorinated lithium-type phosphate-based compound, and a fluorinated lithium-type borate-based compound.
A lithium secondary battery comprising the non-aqueous electrolyte for a lithium secondary battery of claim 1.